Optical forces are applied in optical trapping, for example in optical tweezers. The effects of propelling microspheres in water due to evanescent fields are known. Weakly pronounced resonant peaks of optical forces have been observed in microdroplets. Some evidence for resonance force enhancement has been obtained in waveguide couplers and in the case of off-axially shifted focused beams. Using numerical modeling, high peak-to-background force ratios have been demonstrated in evanescent prism couplers. However, only a small enhancement in the optical force has been observed in the previous work. Although the possibility of using resonant optical forces was recognized, practical devices for sorting microspheres have not been previously proposed or developed.